The present invention relates to a system for defining graphic patterns for a numerical control apparatus.
For driving machine tools under the control of numerical control apparatus (hereinafter referred to as "NC apparatus"), it is general practice to store in a memory unit various data, such as, for example, the paths of movement of the tool of the machine tool, the positions where the tool is to operate on the workpiece, and the operations to be effected by the tool on the workpiece at these positions, the data being entered through an input unit of the NC apparatus. These data are computed and processed in a control unit and an arithmetic unit and the results are delivered through an output unit to a tool actuator.
Numerically controlled machine tools (hereinafter referred to as "NC machine tools") controlled by the NC apparatus are given a tool position with respect to a workpiece under the command of numerical information, and are controlled by the results of arithmetic operations effected by the NC apparatus to enable the tool to machine the workpiece. NC machine tools can machine workpieces into complex configurations with ease and high precision at a high rate of production.
The NC machine tool is generally constructed as shown in FIG. 1 of the accompanying drawings. The NC machine tool basically comprises an NC apparatus 20 for computing numerical information commands supplied from an external source through an input terminal 10 and a machine tool 30 controlled by the results of arithmetic operations effected in the NC apparatus 20. The NC apparatus 20 is composed of an input unit 21 to which external commands are supplied, an arithmetic unit 22 for computing the commands delivered from the input unit 21, a memory unit 23 for storing the results of the arithmetic operations of the arithmetic unit 22 and the commands from the input unit 21, and other information, a control unit 24 for controlling the arithmetic operations of the arithmetic unit 22, and an output unit 25 for issuing computed values such as the results of the arithmetic operations of the arithmetic unit 22. The machine tool 30 has a tool 31 attached to a tool holder 32 mounted on the chuck of a spindle 33 rotated by a spindle motor 34 driven by signals issued from the output unit 25 of the NC apparatus 20.
A workpiece 40 to be machined by the machine tool 30 is fixed by jigs or the like to a table 35 of the machine tool 30. The machine tool 30 also includes a ball screw 36 for moving the table 35 in the direction of the X axis. The ball screw 36 is driven by an X-axis motor 38 through a gear box 37, the X-axis motor 38 being driven by signals from the output unit 25 of the NC apparatus 20. The machine tool 30 also includes mechanisms (not shown), identical to the X-axis drive motor 38 and the ball screw 36 for moving the table 35 in the directions of Y- and Z-axes. These mechanisms are also driven by signals supplied from the NC apparatus 20.
The following means have been employed for entering, through the input unit 21 of the NC apparatus 20, the graphic patterns to be followed by the tool or the machining positions to be taken by the tool, of the NC machine.
More specifically, the following elements are known for defining the graphic patterns to be followed by the tool:
Example 1. Linear interpolation (FIG. 2) G01 Xx1 Yy1 Ff1;
Example 2. Circular interpolation (Arc with a designated radius, FIG. 3) G02 (G03) Xx1 Yy1 Rr1 Ff1;
Example 3. Circular interpolation (Arc with designated coordinates of the arc center, FIG. 4) G02 (G03) Xx1 Yy1 Ii1 Jj1 Ff1.
FIGS. 2 through 4 are illustrative of Examples 1 through 3, and designated at x0, y0 are the coordinates of a starting point, x1, y1 the coordinates of an ending point, r1 a radius, i1, j1 the coordinates of the arc center. In each of the examples, f1 represents the feed speed.
Where the straight line of Example 1 shown in FIG. 2 is to be defined, there are employed a symbol G01 which indicates a straight line, the coordinates Xx1, Yy1 of an ending point of the line, and a feed speed Ff1 for the tool. The arcs can be defined in a similar manner. Symbols G02, G03 used in Examples 2, 3 are G codes indicating arcs or circular interpolation. The code G02 represents clockwise rotation of the tool, and the code G03 represents counterclockwise rotation of the tool. Therefore, the arrowheads on the arcs illustrated in FIGS. 3 and 4 indicate the code G02 (clockwise rotation).
In FIG. 3, two arcs are plotted which interconnect the starting point (x0, y0) and the ending point (x1, y1). These two arcs are distinguished by whether the sign of the radius is positive or negative. If the sign of the radius is positive, then the arc to be drawn is smaller than a semicircle, and if the sign of the radius is negative, then the arc is greater than a semicircle.
Thus, graphic patterns have been defined by entering G codes having various meanings, the coordinates of the ending points of the lines, tool feed speeds, and arc radii in the form of numerical information as illustrated in Examples 1 through 3.
With the conventional graphic pattern definition system, it is necessary to designate the coordinates of ending points, and thus these data need to be known prior to being entered into the NC apparatus. Where the graphic pattern to be entered is complex, intersection computation to find the coordinates of the ending points involves an increased expenditure of time and labor. The addresses X, Y, R, I, J have to be entered each time the numerical values are to be set, thus requiring extra keyboarding operations.
There have been known methods (shown in FIGS. 5 and 6) for defining the machining positions for a tool as a group of points. The definition of such machining positions as a group of points is employed for an NC apparatus for driving a machine tool such as a machining center to bore or tap a workpiece at the positions indicated by the group of points. FIG. 5 is illustrative of a group of points entered as arranged in a row, and FIG. 6 is illustrative of a group of points entered as arranged in a grid-like pattern.
For the row of points shown in FIG. 5, data are entered in the NC apparatus in the form of numerical information: G35XxYyIt1J01Kn1*. G35 is a G code for designating a line at an angle, meaning a straight line inclined at a prescribed angle with respect to a reference line. Designated at X, Y are addresses indicative of the coordinates of a starting point, I an address indicative of the pitch or point-to-point interval t1, J an address indicative of the angle .theta.1 formed between the line passing through the row of points and the X axis, and K is an address representing the number of machining positions required.
For the grid-like dot pattern illustrated in FIG. 6, numerical information: G37XxYyIt1Pn1Jt2Kn2* is employed to enter data in the NC apparatus. G37 is a G code designating a grid, and indicates a group of points to be plotted in a grid-like pattern. Designated in this information labeled by G37 are X, Y address indicating the coordinates of a starting point, I an address indicative of the pitch or point-to-point interval in the direction of the X axis, P an address representative of the number of machining positions in the X-axis direction, J an address representing the pitch or point-to-point interval in the direction of the Y axis, and K an address representative of the number of machining positions in the Y-axis direction.
With the foregoing definition of groups of points, the addresses used have to be entered simultaneously with the numerical values needed. While "J" in the information group headed by G35 is indicative of the angle with respect to the X axis, the same symbol indicates the pitch in the Y-axis direction in the information group headed by G37. Therefore, the same address signal has different meanings which are difficult to discriminate.